恶心需求又来啦！老总需要在商品列表顶部添加一个banner，并且添加分类标识按钮，要求滑动UICollectionView的时候banner滑动，而分类标识按钮悬停（最后有图）

方法步骤：
1.先创建UICollectionView
UICollectionViewFlowLayout * layout = [[UICollectionViewFlowLayout alloc]init];
layout.sectionHeadersPinToVisibleBounds = YES;//头视图悬浮
metal_collection = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 40, SCREEN_WDITH, 0) collectionViewLayout:layout];
metal_collection.backgroundColor = [UIColor clearColor];
metal_collection.delegate = self;
metal_collection.dataSource = self;
metal_collection.bounces = YES;
metal_collection.alwaysBounceVertical = YES;//数据不够也可以垂直滑动
metal_collection.showsVerticalScrollIndicator = YES;
[self.view addSubview:metal_collection];
[metal_collection registerClass:[TMetalProductCell class] forCellWithReuseIdentifier:@"MetalCollectionCell"];
[metal_collection registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"MetalCollectionHead"];
[metal_collection registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"MetalCollectionFooter"];
2.实现代理方法

pragma -------------UICollectionDataSource-------------

-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return 2;//这里很关键，分两组，把banner放在第一组的footer，把分类按钮放在第二组的header
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
if (section == 0) {
return 0;
}
return metal_Muarry.count;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
TMetalProductCell * cell = [metal_collection dequeueReusableCellWithReuseIdentifier:@"MetalCollectionCell" forIndexPath:indexPath];
cell.metalModel = metal_Muarry[indexPath.item];
return cell;
}

pragma -------------UICollectionDelegateFlowLayout-------------

-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
if (section == 1) {
return CGSizeMake(SCREEN_WDITH, 45);
}
return CGSizeZero;
}
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
{
if (section == 0) {
return CGSizeMake(SCREEN_WDITH, 150);
}
return CGSizeZero;
}

• (CGSize)collectionView:(UICollectionView )collectionView layout:(UICollectionViewLayout)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
  {
  if (indexPath.section == 1) {
  return CGSizeMake((SCREEN_WDITH - 5)/2, (SCREEN_WDITH - 5)/2 + 83);
  }
  return CGSizeZero;
  }
• (CGFloat)collectionView:(UICollectionView )collectionView layout:(UICollectionViewLayout)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
  {
  return 5;
  }
• (CGFloat)collectionView:(UICollectionView )collectionView layout:(UICollectionViewLayout)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
  {
  return 5;
  }

pragma -------------UICollectionDelegate-------------

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
TMetalProductModel * model = metal_Muarry[indexPath.item];
TMetalProductDetailVC * transForVC = [[TMetalProductDetailVC alloc]init];
transForVC.metal_id = model.merchId;
[self.navigationController pushViewController:transForVC animated:YES];
}
-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString )kind atIndexPath:(NSIndexPath)indexPath
{
if ([kind isEqualToString:UICollectionElementKindSectionFooter] && indexPath.section == 0) {
UICollectionReusableView * footerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"MetalCollectionFooter" forIndexPath:indexPath];
if (footerView.subviews.count == 0) {//加一个限制，避免无限创建新的
banner_Sc = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WDITH, 150)];
banner_Sc.backgroundColor = [UIColor clearColor];
banner_Sc.showsVerticalScrollIndicator = NO;
banner_Sc.showsHorizontalScrollIndicator = NO;
banner_Sc.pagingEnabled = YES;
banner_Sc.delegate = self;
[footerView addSubview:banner_Sc];
}
return footerView;
}else if ([kind isEqualToString:UICollectionElementKindSectionHeader] && indexPath.section == 1){
UICollectionReusableView * headView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"MetalCollectionHead" forIndexPath:indexPath];
if (headView.subviews.count == 0) {//加一个限制，避免无限创建新的
HTScrollMenuView * menuView = [[HTScrollMenuView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WDITH, 40) withItem:@[@"工艺类",@"钱币类",@"首饰类",@"投资类"] withDelegate:self];
[headView addSubview:menuView];
}
return headView;
}
return nil;
}
OK，至此大功告成！比起网上很多通过contentofset.y来滑动判断方便多了。